1. Field of the Invention
The present invention relates to an ink-jet recording device and a dot-pattern recording method.
2. Description of the Related Art
Heretofore, there have been recording devices for recording an image by forming a dot pattern based on image information on a recording medium such as paper or a plastic thin plate or the like.
Such recording devices employ various types of recording methods such as the ink-jet method, wire-dot method, thermal method, laser beam method or the like, but in recent years, high-speed recording, high image-quality (high resolution), low noise, and so forth have been demanded. As for recording devices corresponding to these demands, there are ink-jet recording devices. Ink-jet recording devices form an image by adhering ink (recording liquid) droplets discharged from the discharge orifices of a recording head to a recording medium.
Also, ink-jet recording devices can perform non-contact recording, and so can record a stable image as to a wide range of a recording medium. Also, with ink-jet recording devices, serial-type ink-jet recording devices mounting a recoding head which reciprocates perpendicular to the transportation direction of a recording medium have been widely known. In the case of serial-type ink-jet recording devices, the size of a recording head can be reduced as compared with line-type ink-jet recording devices. In addition, there are advantages such as being capable of corresponding to the size of various types of a recording medium, facilitating multiple colorizing due to having multiple nozzle rows, facilitating adjustment of speed and recording image quality by the number of times of over-write printing, and so forth. However, on the other hand, with serial printers, in the case of printing vertical linework, the linework for each line printed sometimes causes a leaning linework deviation. This is because in the event that the recording head has not been correctly positioned at a carriage, ink discharge orifices may be disposed leaning from a normal position, and the recording dot row thereof is recorded leaning (e.g., slanted away from the vertical) in the transportation direction of the recording medium. Further, such a recording positional deviation destroys the complementary relation between the respective recording scans in the case of performing multi-pass recording, resulting in deterioration of image quality. Further, with a recording device which performs color printing by disposing such a plurality of heads, and recording a different colored ink at each head, even a small deviation causes irregular color and graininess, resulting in a greatly adverse effect upon an image. Heretofore, with such a serial-type recording device, various types of recording method have been proposed for suppressing an adverse affect upon image quality due to leaning, and improving image quality.
For example, a recording dot row is prevented from leaning (slanting) by improving accuracy regarding a head manufacturing error and a head mounting error as to a recording device. Japanese Patent Laid-Open No. 1995-309007 has proposed an ink-jet printing system for visually reducing a rotational error due to rotation of a head by providing an error correcting circuit for adding offset to a recording image within a nozzle. Japanese Patent Laid-Open No. 1995-40551 has proposed an ink-jet recording device for performing modification of a driving block sequence and modification of a block interval depending on a leaning of a recording head. Japanese Patent Laid-Open No. 1999-240143 has proposed a recording method for determining offset based on the deviation of an impact position in the traversing direction between the nozzle lowermost portion at a first scanning and the nozzle uppermost portion at a second scanning, and shifting a part within the nozzle for the amount of distance depending on the determined offset to correct a head mounting error in the rotational direction at the time of mounting a head. Japanese Patent Laid-Open No. 2004-9489 has proposed an ink-jet recording device which varies data to be assigned to a nozzle depending on the leaning of a head. The above conventional techniques focus on performing preferred control based on assuming that the leaning of a head has been recognized. Incidentally, a method for determining the leaning of a head has been disclosed in Japanese Patent Laid-Open No. 2003-53961. Here, in order to determine the leaning of a printing head as to the sheet-feeding direction, an arrangement for printing a test pattern has been disclosed. First, a part of the printing head at the upstream side in the sheet-feeding direction is moved to print a first pattern while scanning a carriage. Then, a predetermined amount of sheet feeding is performed. Next, a part of the printing head at the downstream side in the sheet-feeding direction, i.e., a part of the printing head on the other end is moved to print a second pattern. Sheet feeding is performed so as to print these patterns in the sheet-feeding direction mutually in an overlapping manner. FIG. 8 illustrates the layouts of the print dots in this overlapped portion. In a state in which the printing head has no leaning, the dots are disposed uniformly. On the contrary, in a state in which the printing head has leaning, the dots are not disposed uniformly. Such a non-uniform layout causes irregularities in density upon an overlapped recording region. A user can visually determine the irregularities in density, and can recognize the leaning of the printing head and the degree thereof.
However, of the above leaning correction methods, with correction using data, the correction resolution and the recording resolution become equal, so the deviation of the recording position at a correction position becomes prominent. Raising recording resolution up to a degree in which the deviation of a recording position is not prominently visible to prevent such a situation means that a greater amount of image data is required to be handled at the main unit, resulting in a factor for causing deterioration of recording speed and increase in the cost of the main unit, which is a problem. Also, raising the correction resolution without changing the amount of image data means that correction using driving the head causes a problem wherein multiple driving signals need to be generated and selected to complicate the configuration, which becomes a factor for increase in cost of the main unit. Specific problems in the conventional techniques will be cited below.
Japanese Patent Laid-Open No. 1995-309007 has proposed the ink-jet printing system for classifying the inside of the printing head into two or more nozzle groups, offsetting the second nozzle group as to the first nozzle group, and recording this to correct an error due to rotation of the head. As for methods for offsetting a nozzle group, “control for shifting a driving signal as to the second nozzle group”, and “control for shifting data itself to be sent to the second nozzle group” have been disclosed in the embodiments. However, in the case of the former control for shifting a driving signal, a problem arises in that driving signal propagating lines for the respective nozzle groups are necessary. Additionally, the maximum width which can be shifted is restricted to a zone until the next data signal is input, and so forth. On the other hand, in the case of the latter control for shifting data itself, the shift distance is not restricted, but another problem is caused wherein attempting to perform fine shifting causes resolution to be increased, resulting in increase of the amount of image data. The problems such as described above both lead to complication of the configuration of the recording device and increase of the amount of memory, resulting in factors for increase in cost.
Japanese Patent Laid-Open No. 1995-40551 has disclosed the ink-jet recording device for performing modification of a driving block sequence and modification of a block interval depending on a leaning of a recording head. However, such control using a driving block causes a problem wherein the maximum width which can be shifted is restricted to a zone until the next data signal is input, which can correspond to a certain leaning alone.
Japanese Patent Laid-Open No. 1999-240143 has proposed the following method for correcting an error due to rotation of a head. This method is a method for determining offset based on the deviation of an impact position in the traversing direction between the nozzle lowermost portion at a first scanning and the nozzle uppermost portion at a second scanning, and shifting a part within a nozzle for the amount of distance depending on the determined offset.
Also, Japanese Patent Laid-Open No. 2004-9489 has disclosed an ink-jet recording device which varies data to be assigned to a nozzle depending on the leaning of a head. However, both of Japanese Patent Laid-Open No. 1999-240143 and Japanese Patent Laid-Open No. 2004-9489 realize shifting of a recording dot position by correcting data. Accordingly, when attempting to perform fine offsetting such as described above, there is the need to increase resolution, which causes a problem wherein the amount of image data becomes great.
The above preceding techniques aim at control of the driving timing of the head assuming that there is information regarding the leaning of the head. Accordingly, how to obtain the amount of the leaning of the head has not been disclosed. Japanese Patent Laid-Open No. 1995-309007 has no description how to obtain the leaning of a printing head. Similarly, Japanese Patent Laid-Open No. 1995-40551 has not disclosed a method for obtaining the leaning of a printing head either. Japanese Patent Laid-Open No. 1999-240143 has proposed the recording method for determining offset based on the deviation of an impact position in the traversing direction between the nozzle lowermost portion at a first scanning and the nozzle uppermost portion at a second scanning, and shifting a part within a nozzle for the amount of distance depending on the determined offset. However, a technique for determining the deviation of an impact position in the traverse direction thereof from one dot printed from the respective nozzles at the upper and lower ends has not been described. Even if the deviation of an impact position is determined, it is not easy to determine the deviation from one dot on a recording sheet. Also, it can be conceived to employ an optical sensor for obtaining the deviation of a recording dot, but which leads to increase in cost and complication of the device configuration. Japanese Patent Laid-Open No. 2003-53961 discloses recognizing a leaning of a printing head using a test pattern. However, the conventional technique for visually determining the irregularities of density of a test pattern sometimes has a problem in that irregularities cannot be readily recognized.